Field of the Invention
Embodiments of the present disclosure relate generally to power conversion and, in particular, to deriving a resonant current signal for controlling controlling a resonant tank current in a resonant converter.
Description of the Related Art
Resonant converters provide many advantages over other types of power converters. Such advantages may include low noise, low component stress, low component count, and predictable conduction-dominated losses. Resonant converters may therefore be smaller, less costly, and more efficient devices that other types of converters.
The resonant converters typically comprise a bridge circuit, a resonant tank circuit, a transformer, and a current transformer (CT). The converter arrangement typically uses the CT to monitor a resonant tank current. The CT is able to generate a high quality signal that accurately represents the tank current flowing through the resonant tank circuit based on the high bandwidth afforded by the CT. While the CT provides galvanic isolation and reduces noise in the measured signal, the CT undesirably raises the cost of parts and space requirements.
Alternatively, the tank current may also be measured based on a simple resistive current shunt resistor. But, the voltage generated across any resistor for current sensing would need to be kept low to minimize unnecessary resistive losses. Hence, any current shunt signal is likely to be in the millivolt range which is troublesome as the resistive shunt will be subjected to common mode noise and high input voltage being fed into the converter. Using a resistive shunt to monitor the resonant tank current is challenging as any monitoring circuit must measure the voltage using a low signal to noise ratio (SNR).
Thus, there is a need for a method and apparatus for easily measuring current within a resonant tank of a resonant power converter at low cost.